Petrography and Petrochemistry of Metamorphic and Igneous Rocks of the “Yeniseyskiy” Site

In 2023, geological exploration of the “Yeniseyskiy” site (Krasnoyarsk Region), where a deep geological repository for radioactive waste (DGR) is planned, resumed. A detailed characterization of the rock composition, particularly tectonic faults as potential radionuclide migration pathways, is critical to ensuring the long-term safety of the site. The aim of the study was to classify the most significant structural elements of the site's rock mass in terms of mineral-deformational transformations, as well as to petrochemically characterize ancient metamorphic rocks and dike complex rocks to elucidate their genesis. The study is based on a comprehensive core analysis of 10 boreholes (up to 150 m deep), including petrographic analysis of thin sections, atomic emission spectrometry to determine the main oxides and rare earth elements, and statistical data processing. Two types of mineral-deformational transformations were identified. Type I (high- and medium-temperature) is associated with healed prototectonics zones, which are similar in properties to the unaltered massif. Type II (low-temperature) formed during hydrothermal-metasomatic transformations and characterizes potentially permeable paleotectonic faults. A schematic geological model has been constructed, including a classification of tectonic fault zones based on an analysis of these mineral-deformation transformations. Petrochemically, it has been established that gneisses (up to 80% of the section) are pararocks formed after graywackes and pelites in an active continental margin setting. Dolerites (17%) are classified as intraplate formations of the continental rift, and newly identified lamprophyres (3%) are calc-alkaline. The completed classification of tectonic faults allows them to be differentiated by their hydrogeological significance: zones with Type I transformations are considered conditionally impermeable, while crushed zones with Type II transformations require detailed hydrogeological monitoring as potential migration routes. The petrochemical data obtained on the genesis of the rocks form the basis for constructing geological and geomechanical models to justify the safety of the DGR.